Apparatus for monitoring the filling factor of containers for compressed gas

ABSTRACT

A gas supply plant particularly for use in supplying an insulating gaseous medium such as SF6 to a switching installation insulated with the gas includes a storage container receiving the gas in a pressurized state from a compressor drawing gas from the low pressure side of the switching installation and adapted to deliver the gas to the high pressure side of the switching installation. A heated ancillary pressurized gas container for supplying make-up gas is connected to the storage container by a pipe line containing a control valve and operation of this valve is controlled by conjointly acting signals derived respectively from the pressure of the medium within the storage container and its state.

United States Patent 1 [111 3,868,963

Muellerpoths 1 Mar. 4, 1975 1 APPARATUS FOR MONITORING THE 2.590.0613/1952 Ash 137/4875 x FILLING FACTOR OF CONTAINERS FOR 2.928.406 3/1960Cunniff l37/4875 UX 2,986,593 5/196] Detrick 62/50 X COMPRESSED GAS3.383.881 5/1968 Bailey 62/50 X [75} Inventor: Reiner Muellerpoths,Schwetzinge 3,770,020 11/1973 Tamuru 137/4875 X Germany [73] AssigneezBBC own Boveri & C p y 11mm [:mmmer Harold W Weakley Limited, Baden,Switzerland [57] ABSTRACT Filedl y 11, 1973 A gas supply plantparticularly for use in supplying an [211 Appl No: 359,424 insulatinggaseous medium such as SF, to a switching installation insulated withthe gas includes a storage container receiving the gas in a pressurizedstate from g pp y Data a compressor drawing gas from the low pressureside May 31. 1972 Germany 2226528 of the switching installation andadapted to deliver the gas to the high pressure side of the switchinginstalla- [52] US. Cl 137/340, l37/l87.5, 62/50 tion. A heated ancillarypressurized gas container for [51] Int. Cl. Fl6k 49/00 supplying make-upgas is connected to the storage [58] Field of Search 137/340, 487.5;62/50 container by a pipe line containing a control valve and operationof this valve is controlled by conjointly act- [56] References Cited ingsignals derived respectively from the pressure of UNITED STATES PATENTSthe medium within the storage container and its state.

2.550.886 5/1951 Thompson 62/50 X 7 Claims, 3 Drawing Figures Thepresent invention relates to a device for monitor-.

ing the extent to which gas containers are filled, especially storagecontainers for SP for use in electrical switch devices insulated withthis gas and for regulating the inflow of SF,, gas from an adjoiningheated SF gas cylinder with a pressure gauge for monitoring the pressurein the storage cylinder.

ln gas supply installations of an encapsulated SF plant, because of thefact that the power switch must be ready for re-operation in a veryshort time after one switching operation has been carried out, it-isnecessary to install a storage container which also serves at the sametime as a buffer container into which it is possible for a compressor topump the gas and which can draw the gas from the low-pressure section ofthe switch. In such installation, losses by leakage are unavoidable sothat after a certain time it is necessary for the storage container tobe topped up once again. Furthermore, it is also possible for losses ofgas to occur as a result of misswitching in the gas supply lines. Theselosses of gas then show themselves in the form of a reduction inpressure in the storage container.

SF has the property of liquefying at a given pressure and at atemperature such as can occur in particular in open air installations.

As a result of such a liquefaction, the pressure falls considerably; bya contact pressure gauge a control order is transmitted to a solenoidvalve to the effect that a further quantity of SF,, should be fed from astorage cylinder to make up for the leakage losses.

However, the problem consists in the fact that the further quantity ofSF fed in liquefies because of the low temperature, so that one cannotmeasure SF sufficient rise in pressure. In the most unfavorableinstance, the storage container can be completely filled with liquidSFG. In order to avoid this, it is necessary to measure not only thepressure but also the temperature; the operator reads from the H graphfor SF gas the maximum pressure which occurs at a given temperature andat which no liquefaction as yet takes place.

However, in order to avoid such an expenditure of labor, it has beenproposed that the storage container should be surrounded by a heatingwinding and that the Sf should be maintained at an adequately hightemperature. However, such a heating winding is troublesome andexpensive.

The problem underlying the invention is that of providing a device ofthe type mentioned above, in which a heating winding is no longerrequired and which auto matically controls a solenoid valve for toppingup with SF depending both on the pressure in the storage vessel and alsoon the liquid level. it is particularly desirable, if the ambienttemperature is very low, to avoid a further unnecessary topping up whichcan lead to even more liquid SF This problem is solved with a device ofthe type mentioned above in that a measuring unit is provided at thelowest position in the storage container which responds to the change inthe physical condition, and which acts on the adjusting member in thesense of a superimposition of the pressure gauge.

In this case the measuring member is advantageously a hot conductorwhich is provided in one branch of a bridge circuit.

In a further form of embodiment, the measuring member used is a platecondenser which is provided in one branch ofa capacitance measuringbridge. Instead ofa circuit arrangement with a hot conductor Or acondenser it is also possible to provide a known float which, when agiven quantity of liquid or a given level Eof liquid is reached in thecontainer, actuates a contact whose output signal can be Switched to anAND member for linking with the measuring impulses of the pressuregauge.

The advantage of the device according to the invention consists in thefact that on the one hand a heating device no longer has to be provided,and that furthermore additional measurements, especially thedetermination of the critical pressure and of the critical temperatureor of the liquefaction pressure and the liquefaction temperature nolonger have to be carried out separately.

A preferred embodiment of the invention will now be explained in detailon thebasis of the accompanying drawing wherein:

FIG. 1 is a diagrammatic view of the improved SF, supply system;

FIG. 2 is a detail showing the hot conductor inserted in a blind hole ofthe SP container; and

FIG. 3 illustrates a modification of the circuit shown in FIG. 1 whereina capacitance bridge is utilized in lieu of a resistance bridge.

With reference now to FIG. 1, a storage vessel 1 for a switchinginstallation insulated with SF not illustrated, receives the SF gasduring normal operation through a pipe 2 coming from a compressor 3,which draws switch-arc contaminated SF via pipe 24 from the low-pressurespace 23 of a switching installation not represented in greater detailand pumps it into the container 1. The contaminated SP gas is purifiedby a filter 4. In order to top up the container 1 in the event of a lossthrough leakage there is provided a further heated container 5 which isinstalled as a storage cylinder. This container 5 is connected via apipe 6 with the storage container 1; in addition there is provided asolenoid valve 7 which opens up the pipe 6 from the container 5 to thecontainer 1 in the event ofa leakage loss. From container 1, there-compressed and filtered gas is led back via pipe 25 to thehigh-pressure space 28 of the switching installation.

Monitoring of the container in accordance with the illustratedembodiment of the invention takes place by means which include a contactpressure gauge 8 and a bridge circuit 9. This bridge circuit 9 includesfour resistances, one of which, resistance 10, the one located on thecontainer, is designed as a hot conductor, whilst the other three, ll,l2, 13, are normal resistances. One diagonal of this bridge is fed bymeans of a source of alternating voltage 14, whilst the drop inpotential on the other diagonal, that is to say at the junction ofresistances 10, 11 and resistances 12, 13, is fed to an amplifier unit15, the output of which energizes the actuating magnet 16 of a relay 17.Relay 17 and another relay 19 together form an AND member, the outputSignal of which controls the solenoid valve 7. That is to say, solenoidvalve 7 is energized and opened to connect the storage cylinder 5 withcontainer 1 only when both relays 17 and 19 are actuated.

if the pressure in the storage container 1 now becomes too low, thecontact pressure gauge 8 responds, and its output signal energizes viaconductor 26 the actuating magnet 18 of a second relay 19 connected inseries with relay 17 via conductor 33. if now at the same time there isa quantity of liquid inside the container, then the relay 17 attractsand opens. Thus while the relay contact 19 is indeed closed, relay 17 isopen with the result that no current can flow through the contacts ofthese relays and through conductor 27 so as to energize and thereby openthe solenoid valve 7.

A temperature-dependent resistance is provided as the hot conductorassociated with container 1. This temperature-dependent resistancechanges its resistance when it is surrounded by liquid SF instead of SPgas. This is because the dissipation of heat in the case of gaseous SFit is therefore necessary to install the hot conductor at the lowestpoint in the storage container 1. which directly actuates the relay 17via a contact. it is also feasible to provide inside the container alight path which utilizes the physical fact that the refractive indexand the light transmissivity of SF gas and SP liquid are differentthereby to sense the dif ference therebetween.

A temperature-dependent resistance 10 is provided,

as the hot conductor associated with container 1. Thistemperature-dependent resistance changes its resistance when it issurrounded by liquid SF instead of SF gas. This is because thedissipation of heat in the case of gaseous SF is less than thedissipation of heat in the case of liquid SF it is therefore necessaryto install the hot conductor at the lowest point in the storagecontainer l.

Advantageously, it is now possible, as shown in FIG. 2 to provide at thelowest point in the inner walla blind hole 20 into which the hotconductor in inserted. For this purpose a-bore is made directly into theblind hole from the outside, the hot conductor rests in this bore andextends into the blind hole. The leads are brought out through theaperture 21. To seal the container a threaded plug 22 is screwed in.

instead of a resistance bridge it is naturally also possible to providea condenser bridge; particularly since the dielectric constant e ofliquid SF differs from the dielectric constant e of gaseous SP For thisreason the sensing condenser which is located inside the SP container atits lowest point is designed as a plate condenser so that itscapacitance which depends upon the dielectric constant will changedependent upon whether the SF between thecondenser plates is in a liquidor gaseous state. FlG. 3 illustrates the use ofa capacitance bridgecircuit 29 from which it will be seen that plate condenser 30 is locatedin the same position as hot conductor 10 in the FIG. 1 bridge circuitwhereas condensers 31, 32, and 33 in the capacitance bridge correspondto resistors 11, 12 and 13 of the resistance bridge circuit of FIG. 1.

However, it is also possible to provide other arrangements; inparticular it is possible to fit a float into the container l whichdirectly actuates the relay 17 via a contact. It is also feasible toprovide inside the container a light path which utilizes the physicalfact that the refractive index and the light transmissivity of SF gasand SF liquid are different thereby to sense the differencetherebetween.

I claim:

1. A gas supply plant particularly for use in supplying an insulatinggaseous medium such as SF to a switching installation insulated with thegas comprising a storage container receiving the gas in a pressurizedstate from a compressorv drawing gas from the low pressure side of theswitching installation and adapted to deliver the gas to the highpressure side of the switching installation, a heated ancillarypressurized gas container connected to said storage container by a pipeline including a control valve therein, a pressure gauge connected withsaid storage container for monitoring the gas pressure therein and whichdelivers a first control signal when the gas pressure falls to apredetermined level, a state measuring member located at the lowest partof said storage container and which is responsive to changes in thephysical state of the medium therein from its gaseous state to itsliquid state to produce a corresponding second control signal, andcontrol means actuated by said first and second control signals actingconjointly to control the opening and closing operations of said controlvalve in said pipe line interconnecting said ancillary container to saidstorage container.

2. A gas supply plant as defined in claim 1, wherein said statemeasuring member located at the lowest part of said storage containerand which responds to a change in physical state of the insulatingmedium therein is constituted by a hot conductor.

3. A gas supply plant as defined in claim 2 wherein said hot conductorforms the measuring branch of an electrical resistance bridge circuit.

4. A gas supply plant as defined in claim 1 wherein said state measuringmember located at the lowest part of said storage container and whichresponds to a change in physical state of the insulating medium thereinis constituted by an electrical condenser of the plate type.

5. A gas supply plant as defined in claim 4 wherein said plate condenserforms the measuring branch of an electrical capacitance measuringbridge.

6. A gas supply plant as defined in claim 1 wherein the lowest part ofsaid storage container is provided with a blind hole in which said statemeasuring member is located.

7. A gas supply plant as defined in claim 1 wherein said control valveis of the solenoid type and is connected to an energizing source throughcontacts of two relays arranged in series, said relays being controlledrespectively by said first and second control signals.

* l l= l

1. A GAS SUPPLY PARTICULARLY FOR USE IN SUPPLYING AN INSULATING GASEOUSMEDIUM SUCH AS SF6 TO SWITCHING INSTALLATION INSULATED WITH THE GASCOMPRISING A STORAGE CONTAINER RECEIVING THE GAS IN A PRESSURIZED STATEFROM A COMPRESSOR DRAWING GAS FROM THE LOW PRESSURE SIDE OF THESWITCHING INSTALLATION AND ADAPTED TO DELIVER THE GAS TO THE HIGHPRESSURE SIDE OF THE SWITCHING INSTALLATION, A HEATED ANCILLARYPRESSURIZED GAS CONTAINER CONNECTED TO SAID STORAGE CONTAINER BY A PIPELINE INCLUDING A CONTROL VALUE THEREIN, A PRESSURE GAUGE CONNECTED WITHSAID STORAGE CONTAINER FOR MONITORING THE GAS PRESSURE THEREIN AND WHICHDELIVERS A FIRST CONTROL SIGNAL WHEN THE GAS PRESSURE FALLS TO APREDETERMINED LEVEL, A STATE MEASURING MEMBER LOCATED AT THE LOWER PARTOF SAID STORAGE CONTAINER AND WHICH IS RESPONSIVE TO CHANGES IN THEPHYSICAL STATE OF THE MEDIUM THEREIN FROM ITS GASEOUS STATE TO ITSLIQUID STATE TO PRODUCE A CORRESPONDING SECOND CONTROL SIGNAL, ANDCONTROL MEANS ACTUATED BY SAID FIRST AND SECOND CONTROL SIGNALS ACTINGCONJOINTLY TO CONTROL THE OPENING AND CLOSING OPERATIONS OF SAID CONTROLVALUE IN SAID PIPE LINE INTERCONNECTING SAID ANCILLARY CONTAINER TO SAIDSTORAGE CONTAINER.
 2. A gas supply plant as defined in claim 1, whereinsaid state measuring member located at the lowest part of said storagecontainer and which responds to a change in physical state of theinsulating medium therein is constituted by a hot conductor.
 3. A gassupply plant as defined in claim 2 wherein said hot conductor forms themeasuring branch of an electrical resistance bridge circuit.
 4. A gassupply plant as defined in claim 1 wherein said state measuring memberlocated at the lowest part of said storage container and which respondsto a change in physical state of the insulating medium therein isconstituted by an electrical condenser of the plate type.
 5. A gassupply plant as defined in claim 4 wherein said plate condenser formsthe measuring branch of an electrical capacitance measuring bridge.
 6. Agas supply plant as defined in claim 1 wherein the lowest part of saidstorage container is provided with a blind hole in which said statemeasuring member is located.
 7. A gas supply plant as defined in claim 1wherein said control valve is of the solenoid type and is connected toan energizing source through contacts of two relays arranged in series,said relays being controlled respectively by said first and secondcontrol signals.